Increased throughput in melt fabrication and foaming of polyester

Abstract

Disclosed is a process for obtaining polyester articles, including foamed articles, containing low levels of extractable branching agent. The process comprises: (1) forming a molten mixture comprising (i) a major amount of a first resin composition comprising polyester and from 0 up to about 1 wt. % of a compound capable of branching the polyester, and (ii) a minor amount of a second polyester resin composition comprising at least about 50 wt. % polyester resin and greater than about 2 wt. % of a compound capable of branching the polyester, wherein the relative amounts of (i) and (ii) are such that said molten mixture comprises from about 0.1 wt. % to about 1 wt. % of said branching compound; (2) adding a blowing agent to the molten mixture; and (3) extruding the resultant mixture to obtain a foam. The invention is also directed to the second composition used in the above process, and foamed polyester articles obtained from the process.

We claim: 
     
       1. A process for melt processing polyester comprising: (1) forming a molten mixture comprising (i) a major amount of a first polyester resin composition comprising polyester and from 0 up to about 1 wt. % of a polyester branching compound, and (ii) a minor amount of a second polyester resin composition comprising at least about 50 wt. % polyester resin and greater than about 5 wt. % of said branching compound; said molten mixture comprising from about 0.1 wt. % to about 1 wt. % of said branching compound;   (2) melt-processing the resultant molten mixture under conditions of time and temperature sufficient to enhance the melt strength of the mixture; and   (3) directly fabricating the molten mixture into a film, sheet, injection molded article, or blow molded article.   
     
     
       2. The process of claim 1 wherein melt processing is carrier out for about 1 to about 20 minutes at a temperature of from about 240° to about 310° C. 
     
     
       3. The process of claim 1 wherein the polyester in said first and said second polyester resin compositions is at least one member selected from the group consisting of polyalkylene terephthalate and polyalkylene naphthalate, and said branching compound present in the second polyester resin composition is selected from compounds having two or more acid anhydride groups per molecule. 
     
     
       4. The process of claim 1 wherein said first composition comprises polyethylene terephthalate, the branching compound present in said second polyester composition comprises pyromellitic dianhydride, and said branching compound constitutes from about 8 to about 12 wt. % of said second polyester composition.